title: Contraction mode shift in quadriceps femoris muscle activation during dynamic knee extensor exercise with increasing loads.
abstract: The objective of the present study was to examine the superficial quadriceps femoris (QF) muscle electromyogram (EMG) during dynamic sub-maximal knee extension exercise between young adult men and women. Thirty subjects completed, in a random order, 2 sub-maximal repetitions of single-leg knee extensions at 20-90% of their one-repetition maximum (1RM). Vastus medialis (VM), vastus lateralis (VL) and rectus femoris (RF) muscle integrated EMG (IEMG) during each sub-maximal lift was normalized to the respective 1RM for concentric, isometric and eccentric modes. The EMG median frequency (f(med)) was determined over the isometric mode. Men attained a significantly (p<0.05) greater knee angular velocity than the women during the concentric mode (83.6+/-19.1 degrees /s and 67.4+/-19.8 degrees /s, respectively). RF IEMG was significantly lesser than the VM (p=0.014) and VL (p<0.001) muscles, when collapsed across all contraction modes, loads, and sex. Overall IEMG was significantly greater during the concentric (p<0.001) and isometric (p<0.001) modes, than the eccentric mode. Men generated significantly (p=0.03) greater VL muscle IEMG than the women, while the opposite pattern emerged for the RF muscle. VM f(med) (105.1+/-11.1Hz) was significantly lesser than the VL (180.3+/-19.5Hz) and RF (127.7+/-13.9Hz) muscles across all lifting intensities, while the men (137.7+/-10.7Hz) generated greater values than the women (129.0+/-11.4Hz). The findings demonstrate a reduction in QF muscle activation across the concentric to eccentric transition, which may be related to the mode-specific velocity pattern.
authors.affiliation: Human Performance and Fatigue Laboratory, Department of Kinesiology, The University of Toledo, Mail Stop 201, Toledo, OH 43606, USA. danny.pincivero@utoledo.edu
authors.forename: Danny M
authors.initials: DM
authors.lastname: Pincivero
authors.forename: Alan J
authors.initials: AJ
authors.lastname: Coelho
authors.forename: Robert M
authors.initials: RM
authors.lastname: Campy
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology; D000328:Adult; D004576:Electromyography / Q000379:methods; D005080:Exercise Test; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000502:physiology*; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*